The present invention relates generally to systems, arrangements and methods for tracking the position of and/or guiding an underground boring tool during its operation and more particularly to tracking the position of the boring tool within a coordinate system using magnetic field intensity measurements either alone or in combination with certain physically measurable parameters. Positional information may then be used in remotely guiding the boring tool.
As will be described in more detail hereinafter, there are disclosed herein arrangements, specific apparatus and associated methods for use in tracking and/or guiding the movement and certain orientation parameters of an underground boring tool in a region of ground. In the method and arrangements of the present invention, the boring tool is provided with means for transmitting an electromagnetic field. One or more detectors are provided, each having an electromagnetic field receiving antenna assembly including at least one antenna. Each detector is located at a fixed position and at a particular orientation within the region of ground but not necessarily along the intended path of movement of the boring tool. The position and particular orientation of the antenna(s) associated with each detector provided is determined. The electromagnetic field is then transmitted from the boring tool when the boring tool is at certain positions on the path for receipt by the detectors. When the boring tool is at a first point on the path, its position is established along with the aforementioned certain orientation parameters of the boring tool. After moving the boring tool along the path which includes the first point and at least to a subsequent second point, at least one component of the intensity of the electromagnetic field is measured using the detector or detectors and the position of the boring tool at the second point is determined, at least to an approximation, using as an input the electromagnetic field intensity measurement or measurements taken by the one or more detectors when the boring tool is at the second point.
In accordance with one embodiment of the present invention, which may be referred to as a dead reckoning approach, only one detector is required for acquiring the magnetic field intensity measurements wherein at least one measurement is required.
In accordance with another embodiment of the present invention, which may be referred to as a position determination approach, at least two detectors arc required for acquiring the magnetic field intensity measurements wherein at least five magnetic measurements are required in an implementation wherein only magnetic measurements are relied on in locating the boring tool.
In either of the aforementioned embodiments, physically measurable values may be utilized in conjunction with magnetic measurements. In one technique, which is particularly useful in the dead reckoning approach, underground movement of the boring tool is determined in a specific way at the drill rig, with which the boring tool is connected by a drill string. This drill string is moved by its engagement with a movable carriage on the drill rig. Thus, movement of the boring tool is determined by monitoring movement of the carriage relative to a fixed location on the drill rig which corresponds with the underground movement of the boring tool. The determined movements of the boring tool may be used in conjunction with magnetic or other measurements to obtain the position of the boring tool. In one feature, a clamping arrangement on the drill rig, which is engaged with the drill string at predetermined times whereby to prevent movement of the drill string, is monitored in a highly advantageous way so as to distinguish between movements of the carriage which change the underground length of the drill string and those which do not change its length.
Apparatus for use in either the dead reckoning approach or the position determination approach may utilize a highly advantageous cubic antenna assembly which is manufactured in accordance with the present invention. The cubic antenna assembly includes support means forming at least a first pair of parallel sides which are spaced apart from one another and a first antenna supported by these first parallel sides so as to define a first antenna pattern along a first axis having a center point on the first axis which is midway between the first parallel sides. A second pair of parallel sides may be provided as part of the support member which are also spaced apart from one another such that a second antenna may be supported by the second pair of parallel sides so as to define a second antenna pattern along a second axis which is orthogonal to the first axis such that the second antenna pattern includes a center point on the second axis which is midway between the second pair of parallel sides and which coincides with the center point of the first antenna pattern. Still a third pair of parallel sides may be provided which are spaced apart from one another such that a third antenna may be supported by the third pair of parallel sides so as to define a third antenna pattern along a third axis which is orthogonal to the first and second axes. The third antenna pattern has a center point on its third axis which is midway between the third pair of parallel sides and which coincides with the center point of the first and second antenna patterns. Irrespective of the number of pairs of sides which support antenna patterns, the support member may be configured in the form of a dielectric cube having a geometric center at which all of the antenna patterns are centered such that the precise location of the center of each of these antenna patterns is known. The ability to precisely position the center of three orthogonal antenna patterns at one point is highly advantageous within the context of the present invention wherein precise positional measurements are contemplated.
In accordance with one aspect of the present invention, a highly advantageous mapping tool instrument is disclosed which is particularly useful in the position determination approach. The mapping tool includes a housing which houses a transmitter for transmitting an electromagnetic setup signal such that the detectors in a system implementation may receive the signal. The detected signal may thereafter, be used in determining the present position of the mapping tool. In one feature, the housing of the mapping tool may be configured for positioning on each detector in a predetermined way such that the orientation of the mapping tool is fixed relative to the detector on which it is so positioned. In another feature, the mapping tool may include means within its housing for determining certain orientation parameters when the mapping tool is positioned on one of the detectors. Such parameters are useful in setting up an array of detectors prior to drilling. In still another feature, these orientation parameters may be displayed on the mapping tool and/or transmitted to another location.